As a part of #7302, MinIO server's (configured with https) response when it
encounters http request has changed from 403 to 400 and the custom message
"SSL Required" is removed.
Accordingly healthcheck script is updated to check for status 400 before
trying https request.
Fixes#7517
Go script makes it easy to read/maintain. Also updated the timeout
in Dockerfiles from 5s to default 30s and test interval to 1m
Higher timeout makes sense as server may sometimes respond slowly
if under high load as reported in #6974Fixes#6974
